Wired radio transmitting system



July 23, 1940. w|E$$NER ET 2,208,916

WIRED RADIO TRANSMITTING SYSTEM Filed Nov. 13.. 1957 [4424/90/19 Spa/7y 4E? Patented July 23, 1940 PATENT OFFICE WIRED RADIO TRANSMITTING SYSTEM Alfred Wiessner and Wolfgang Spang, Berlin,

Germany, assignors to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof, Germany, a com- Application November 13, 1937, Serial No. 174,379 A In Sweden November 27, 1936 7 Claims.

As is well known, broadcast performances, alarm signals and the like may be transmitted over wire lines, such as telephone networks, by means of high frequency carrier currents. For

instance, in an exchange station several pro grammes on different waves maybe conjointly impressed on a subscribers network. In order to obtain agood efficiency of such transmission the transmitting or amplifying devices must be 10 matched to the wire lines. This, however, entails various diificulties. In fact, the lines being. of different lengths, the input amplitudes must differ depending on the lengths of the respective lines in order to obtain sufficiently great amplitudes at the subscribers stations. It has been proposed to arrange the subscribers lines in groups depending on their attenuation or damping effectand to allocate additional high frequency amplifiers to one or a number of such groups. However, in such arrangements thus obtained a plurality of amplifiers must be provided, making surveying and checking difficult. Furthermore, difficulties arise because in the customary transmitting arrangements the lines are fed asymmetrically. For instance, if a transmitter or amplifier of this kind is connected to a network then reception is found to be possible also with respect to those lines upon which on the exchange side no high frequency energy is impressed by means of electric separating filters, the wires not connected to these filters being fed over leakage capacities and the like on account of I asymmetries in the transmitting arrangement.

In accordance with the invention such difficulties are avoided by connecting the lines in stages or groups between which a resistance adaptation is effected. In accordance with another feature of the invention the lines are grouped depending on their attenuation characteristics.

The invention will be understood from the following description, reference being had to the accompanying drawing diagrammatically illustrating one embodiment of the invention.

Suppose, for instance, that a transmitter has to be matched to a plurality of subscribers lines, e. g., 1,000 lines, each of which has an electric separating filter that serves to convey the high connection. The attenuation of the lines may,

55 be distributed in any manner and in accordance with line lengths which are from 0 to 5 kilometres. The problem is to apply the proper, voltage to each of the lines, that is, a voltage suitable from an economic standpoint and adapted also for the reception, and further to Q match all of the lines to the transmitter.

According to the invention the lines are arranged in groups in accordance with their attenuation, for instance in groups of 16 units each, and to each of these groups is added the resistance of one unit of the next group of greater line attenuation. To such end, between the said groups or stages a resistance adaptation must be effected in accordance with the square root of the number of connected members. In the example here assumed a resistance adaptation according to \/16 will thus be necessary. The decrease in the voltage in direction away from the transmitter is inversely proportional to the resistance transformation, that is to say, is pro- ,2 portional to Since the number of the lines comprised in a group determines the voltage transformation, a further feature of the invention provides that the grouping, effected in accordance with thev attenuation of the lines, should be such that the voltage at the line ends be the same in the various groups. In such case the attenuation difference between the groups must be proportional to the natural logarithm of the voltage transformation ratio, that is, proportional'to the natural logarithm of the square root of the number which indicates how many lines are comprised in a group. In the present example this attenuation difference must be proportional to log. nat. \/16.

In the drawing: I denotes a transmitter which is arranged, for instance, as a wide-band amplifier for a plurality of high frequency waves, or which consists of a group of cooperating transmitters which are 45 all of symmetrical construction. To transmitter l, groups 3, 5. l of electric separating filters A are connected by high frequency transformers 2, 4, 6. The filters A of group 3 are connected in parallel to transformer 2, and those of groups 5 are connected in parallel to transformer 4, while the filters A of group I are similarly connected to transformer 6. To each filter A a two-wire line L is joined that belongsto one or several subscribers stations R, such as broadcast rer ceivers or the like. For simplicity only a few of the stations R are shown. Transformer t takes the place of a filter A of group 3, while transformer 6 replaces a filter A of the group 5. In this way 16 units are connected to each transformer, the filters A of group 3 together with transformer 4 being connected to transformer 2, and the filters A of group 5 and transformer 6 being connected to transformer 4 while to transformer 6 the filters A of group 'i are joined. The lines L of group I have a smaller attenuation resistance than those of group 5, while the lines L of group 5 have a smallerattenuatio-n resistance than those of group 3.

Suppose transmitter l to be matched to a load resistance of 150 ohms. The resistance of each filter A is likewise 150' ohms. In order to match the IB members of the group 3' to the transmitter I the transformer 2 must have a transformation ratio of V16, that is, a transformation ratio of 4:1. The filters A of group 5 being connected in parallel are effective only as the sixteenth part of the resistance of 150 ohms. In order to give them the resistance of each filter A of the group 3, transformer 4 must effect a voltage transformation that according to the said number 16 is likewise defined by the ratio 4:1. Since such resistance-transfer causes the voltage to be decreased by the same value the filters. A of group 5 will receive only the fourth part of the voltage applied to the filters A of the group 3. The construction of transformer 6 and the requisite adaptation of voltage and resistances are accomplished in the same manner.

The groups 3, 5, I thus are alike inasmuch as all the filters A have the same input resistance, and they are different from each other inasmuch as in group 3 the attenuation of the lines L is greater than in group 5 while in this group the line attenuation is greater than in group i which thus has the least line attenuation. To group 7 a voltage equal to the fourth part of the voltage of group 5 is applied while the voltage applied to group 5 is equal to the fourth part of the voltageprevailing in group 3.

The attenuation resistances between the groups are so' chosen that the voltage applied to each group will be one-fourth of the voltage applied to the preceding group, i. e., sufficient to ensure that approximately the same tension shall be available at all the subscribers stationsv R.

'The number of serially connected stages or groups is immaterial to the invention. Instead of the individual filters A a group of filters which is associated with lines of correspondingly less attenuation may be arranged. For instance, a filter A of group 5 may be replaced by an additional transformer associated with groups of lines, thus being replaced by an arrangement of the kindshown at 6, l. The manner of accomplishing this depends upon economical and technical considerations which are different depending upon the nature of the networks to be fed.

In accordance with another feature of the invention the output lines are fed perfectly symmetrically, means being provided to prevent the output lines from receiving any energy whatsoever over any leakage capacities or constructional asymmetries. It is known per se to provide for a symmetrical construction of the circuit arrangements of carrier. systems. In prior devices, however, the object ofsuch symmetrical construction was not to feed the lines symmetrically but to suppress in these modulated lines the carrier. No attention has been paid to feeding the lines symmetrically because there is no relation between feeding and modulation. However, experiments have shown that it is just the mode of feeding the output lines which requires consideration especially in the case of cables employed for transmitting communications at high frequency.

It is of particular advantage to have the final stage or final stages of the transmitter connected in push-pull.

The described arrangement has the special advantage that by commingling lines of different attenuation the whole of the network can be advantageously matched to a communication trans: mitter. In the novel arrangement a certain compulsory relation exists between the voltages necessary for the groups and the number of members or units comprised in each group. Apart from this the novel arrangement is of particularly favorable action inasmuch as owing to the use of equivalent filters A the lines connected to these are of the same impedance regardless of their lengths and the attenuation determined by these.

An esential feature of the described arrangement is that all the lines are fed perfectly symmetrically. Preferably these lines are telephone cables over which also low frequency communications may be transmitted. Feeding the lines symmetrically insures that there shall be no influence upon lines not fed with high frequency energy and that therefore high frequency energy can merely be taken from the lines fed therewith. Furthermore, the novel arrangement of the high frequency transformers enables arrangement of the high frequency transformers enables a network to be fed from transmitters or amplifiers without additional high frequency ampli- Y fiers having to be provided even in the case of line groups of very different attenuation.

In the drawing only the high frequency portion of the system is shown, the low frequency portion being omitted for clearness. The arrangement of the low frequency portion is such that the low frequency energy is conveyed to the subscribers lines directly and at a point in advance of the filters A, and that means for separating low frequency from high frequency energy is provided in the subscribers stations too.

What is claimed is:

l. A wired-radio transmitting arrangement comprising a high frequency transmitter, a plurality of successive stages each comprising a group of wire lines associated with the transmitter in successive stages, each stage having greater attenuation than the succeeding stage, and means for matching the resistance of each stage to the succeeding stage, whereby the input amplitude of each stage will be in proportion with its attenuation.

2. The arrangement defined in claim 1 and in which the impedance matching means comprises a high frequency transformer for each group.

3. The arrangement defined in claim 1 and in which the impedance matching means comprises a high frequency transformer for each group symmetrically connected with respect to the units thereof.

4. An arrangement according to claim 1, wherein the wire lines are grouped in accordance with their attenuation and wherein the transmitting voltage of each group thus formed is inversely proportional to the square root of the number of lines of this group.

5. An arrangement according to claim 1. wherein the Wire lines are grouped in accordance with their attenuation and wherein the difference of the attenuation values of the groups thus formed is proportional to the natural logarithm of the voltage transformation ratio.

6. An arrangement according to claim 1 having a plurality of lines connected in parallel in each group, each preceded by an electric separating filter so as to offer the same input impedance, a transformer interconnecting said transmitter and one of said groups, and transformers and transmission lines interconnecting said other groups comprising said successive stages. 7

' 7. An arrangement according to claim 1, wherein each of said stages includes a plurality of transformers, and additional transmission lines for interconnecting said successive stages.

ALFRED WIESSNER. WOLFGANG SPAN G. 

